Dual use - Generac Q-55G Question

I have a motorhome with a Generac Q-55G genset in it. This is a 5.5kW plant that runs on LPG.

Lately, with the storms in Florida, I've been thinking of setting it up to also power our house. This would require a switching arrangement for strapping it for 220V single phase for the house and then back to the 120V for the motorhome.

I got out the manual for the genset to make sure it is possible to do this.

It was then that I learned something new. The generator has two 120 Volt windings and, at first, I thought making the changeover would be simple 'til I saw that they have it hooked-up for two separate 120V outputs. Even stranger is the fact that one of the windings is 30 Amps and the other is 20 amps!

Why did they do it that way? As it is, if I strap it for 120/220, I can only draw 20 Amps or 4400W before popping the breaker. I really need that extra 1.1kW for starting motors, etc.

Since I don't have a wiring diagram of the motorhome, all I can guess is that somehow, the motorhome people can run the A/C off the 30A winding and everything else off the 20A winding. Either that or the 20-Amp winding is not being used at all unless you use the accessory outlet on the genset itself.

If they are running the A/C alone off the 30A winding and everything else off the 20A, how do they have the double pole, double throw automatic shore power/generator relay wired?

Unless someone has a way out of this fix, I think I'll have to scrap my plan to use my motorhome genset as a double-purpose unit.

Any help out there???!!

Take care - Elden

Hi, ** I don't know if I can answer your question directly but maybe this will give some insight. I have a DeVilbiss 5Kw generator that is set up like yours, except that both windings are equal (2500W, 20.8A each). Usually it's tough to parallel or series AC sources because the slightest phase shift will result in hot windings and a loss of power. However, these are apparently so precisely set in the generator housing that the phasing of each stator winding is identical. For 240V 5Kw, a panel switching arrangement puts them in series; for 120V 5Kw, they're in parallel -- or at least they're supposed to be. They did make one mistake, but I'll get to that in a moment. ** At first I couldn't believe they were getting away with that arrangement, but it works! The one area in which they did make a mistake was to set it up so that all 41.6A at 120V ends up funneling through one 20A breaker. Guess what happens. ** I hook the generator up through the 240V buss in the house, but I actually only use 120V in the house with the generator running. Normally in a house with 240V wiring, one leg (Neutral to one Hot) feeds part of the house, the other leg (Neutral to the other Hot) feeds another part. Since this effectively meant that any given high-draw item like a window A/C was trying to start and run on one 2500W winding, I rigged up an external adapter which 'folds' the two 120V output legs together (parallels them externally), and that feeds into the 240V house wiring. This has worked just fine for starting all high-draw motors etc. on all 120V circuits, although of course I can't use anything that runs on 240V with that arrangement. My A/C units are all 120V so that's not a problem. I'm assuming your GenerAC is basically the same, although the current ratings of each winding are different. As long as they're in phase, though, I would think you could parallel them for maximum current at 120V.

Eldun,

I would not recommend what you are suggesting to do for several reasons.

You are correct in that there are two 120 volt windings in the generator. The larger one for the a/c, the smaller for everything else. This is common for larger motorhomes (Onans can be set up the same way)

Don't confuse what you have to a small portable generator, as another writer has. In some portables, you have a choice to either parallel or connect in series the two 120 volt windings, so you can get full output at 120 volts or 240 volts. That is not your circumstance.

If you reconnect the output by paralleling the outputs, you'll have multiple problems. First, the windings are NOT equal, and will not share load equally. One will run hotter than the other, and thus, increase liklihood of a winding failure (Generac windings are frail enough on a good day). Your voltage regulator won't like it either - it will regulate based on the voltage on one winding, and the other will be what it is. So if a good bit of load is one winding one, and the regulator is sensing it, it will have the correct 120 volts. The second winding, with less load, may have dangerously higher voltage, enough to damage things in your house, and your voltage regulator won't even know.

Many generators are designed to operate at 120 or 120/240. Yours is not one of them.

Jim Thomas Former Onan, Generac, Elliott service manager

Jim:

I will take your advice and leave my Generac alone. Most of the time, I heed the advice of experts and you are one.

Now, I'll go a-lookin' for something more suited to my purpose.

I do have an old Onan 5CW (5kW) from about 1950, but it's permanently mounted and wired to a transfer switch in my rural KY home that is on the market right now. The only way I'd remove it is if the buyer really didn't want it.

The old Onan is a real brick, physically about the size of a newer 10kW Onan. I've had it set-up here since about 1974 and it's saved our bacon a few times.

Thanks again!

Take care - Elden